A typical prior art head and disk system 10 is illustrated in FIG. 1. In operation the magnetic transducer 20 is supported by the suspension 13 as it flies above the disk 16. The magnetic transducer 20, usually called a “head” or “slider,” is composed of elements that perform the task of writing magnetic transitions (the write element 23) and reading the magnetic transitions (the read element 12). The electrical signals to and from the read and write head elements 12, 23 travel along conductive paths (leads) 14 which are attached to or embedded in the suspension 13. The magnetic transducer 20 is positioned over points at varying radial distances from the center of the disk 16 to read and write circular tracks (not shown). The disk 16 is attached to a spindle 18 that is driven by a spindle motor 24 to rotate the disk 16. The disk 16 comprises a substrate 26 on which a plurality of thin films 21 are deposited. The thin films 21 include ferromagnetic material in which the write element 23 records the magnetic transitions in which information is encoded. A tape based storage system (not shown) uses a magnetic transducer in essentially the same way as a disk drive, with the moving tape being used in place of the rotating disk 16.
There are several types of read elements 12 including giant magnetoresistive (GMR) and tunnel junction. A spin valve (SV) head is a particular type of GMR head. A typical SV head (not shown) has a pinned ferromagnetic layer and a free ferromagnetic layer separated by a nonmagnetic metal spacer layer. The free ferromagnetic layer functions as the sensor element and is typically a rectangular strip of material with a conductive lead in electrical contact with each side as viewed in a plan view. Various methods of establishing the electrical contact have been described including, for example, butting the leads up against the sensor element at the ends, separating the leads from the sensor by a thin capping layer and overlaying the lead layers on the top surface of the sensor stack which may have a capping layer.
Typically leads (not shown) are made from single layers of copper, rhodium, molybdenum, tungsten, tantalum or gold, but leads with a multilayer structure have been proposed. For example, U.S. Pat. No. 5,438,470 to Ravipati, et al., suggest using a thin layer of tantalum under a layer of gold for the leads. U.S. Pat. No. 5,491,600 to Chen, et al., describes leads with two refractory metal layers sandwiching a highly conductive metal layer. One multilayer embodiment has alternating layers of tantalum and gold. U.S. Pat. No. 5,883,764 to Pinarbasi similarly describes a multilayer lead structure of Ta/Cr/Ta for use with a hard bias layer of CoPtCr.
The need for increased track density in disk drives means that the magnetic sensors must be improved to read from narrower tracks while maintaining the required magnetic stability. There have been some efforts to stabilize very narrow sensor elements by using increasingly thick hard bias structures, but there has been only limited success with this “brute force” approach. One problem with this approach is that it consumes the total gap tolerance for the combined sensor/lead structure leaving little margin for insulating gap layers to provide edge coverage and for electrical insulation from the shields. Consequently these designs require complex mask steps and decrease yield through losses due to shield shorts.
U.S. Pat. No. 5,608,593 to Kim, et al., describes a method of increasing stability of an SV head by forming the free layer in a “mesa structure,” i.e., a shape with a trapezoidal cross section as taken parallel to the ABS. The leads are disposed off to the sides of the free layer and are separated from the free layer by permanent magnet layers.
U.S. Pat. No. 5,654,854 to Mallary describes the use of a sensor with a concave back which is said to provide an effective longitudinal bias field in the center of the active MR element to prevent multi-domain states.